An aircraft wing is normally designed to have a lift/drag (L/D) ratio that is optimized for a particular flight condition. For example, many commercial aircraft are designed to cruise at a particular speed and altitude. The wings of such aircraft are designed so that they have a L/D ratio that is optimized for that design condition. Operation of such aircraft at off design flight conditions thus results in higher fuel consumption or reduced maneuvering performance than that which could otherwise be acheived. Optimization of L/D to achieve maximum performance becomes a substantial problem for the aircraft designer in aircraft that are subjected to wide variations in flight conditions, i.e., changes in speed, altitude, and normal acceleration. Most military aircraft are in this latter category, for example. While the present invention is concerned primarily with this latter case, the instant invention is also applicable to commercial aircraft types.
It is well-known that the L/D ratio of an aircraft wing may be altered by varying the chord-wise curvature or camber of the wing. In conventional wing designs, wing camber is designed in accordance with the particular flight conditions to which the wing will be subjected. By way of example, and referring now to FIG. 1, therein is shown optimum wing cambers for different flight conditions including what is commonly known in the art as high speed dash, cruise, and maneuver conditions. As can be seen, wing camber design for the high speed dash condition 10 is different from the camber for the cruise or maneuver conditions 11, 12. The camber for each wing 10, 11, 12 may be designed so that the L/D ratio is optimized for each respective condition. FIG. 1 shows the relationship of L/D for each wing camber 10, 11, 12. For a wing having variable camber capability that includes a smooth wing upper surface contour, it is possible to achieve the lift to drag L/D relationship indicated by the dashed line 16. The dashed line 16, therefore, represents an envelope of minimum drag or maximum L/D at any given flight condition which can be achieved by varying wing camber. It is beneficial to have an aircraft wing wherein the wing camber can be varied so that the aircraft always operates on the optimum L/D boundary (line 16 of FIG. 1) regardless of the flight condition. Operation along the boundary 16 minimizes aircraft drag and results in increased aircraft range and improvement in aircraft maneuver capability throughout the aircraft flight envelope.
To obtain the above-mentioned benefits, wings having variable camber capability have been designed. Typically, and referring now to the wing 21 in FIG. 2, such wings have at least one movable leading edge surface 22, and one movable trailing edge surface 24, wherein both surfaces 22, 24 are positioned relative to each other so that they can each be moved to vary wing camber while maintaining a smooth upper surface contour. The physical construction of such a wing is well-known in the art and has been described in various U.S. patents including: U.S. Pat. No. 4,351,502 issued to Frank D. Statkus on Sept. 28, 1982; U.S. Pat. No. 3,994,452 issued to James B. Cole on Nov. 30, 1976; U.S. Pat. No. 3,994,451 issued to James B. Cole on Nov. 30, 1976; U.S. Pat. No. 3,930,626 issued to Thomas L. Croswell on Jan. 6, 1976; and U.S. Pat. No. 3,698,668 issued to James B. Cole on Oct. 17, 1972. However, a system for commanding wing camber is not disclosed in these patents.
The present invention is directed towards providing a system for commanding a variable camber wing, to optimize wing L/D for varying flight conditions that may occur during a range of possible aircraft maneuvers and operations. This permits the wing to maintain an optimum L/D relationship like curve 16 shown in FIG. 1. Having such a system has many attendant advantages. For example, such a system may provide improved aircraft maneuverability, increased aircraft range, lower stall speed, improved wing buffet characteristics, and reduced aircraft fuel consumption.